Simple Determination of the Linear Viscoelastic Region of a Polymer Using a Rheometer

Materials such as polymers exhibit viscoelastic behavior which is directly related to molecular structure and formulation differences. To accurately evaluate the relationships between molecular structure and viscoelastic behavior requires that experiments, such as rheological measurements, be conducted in regions where the viscoelastic properties observed are independent of imposed stress or strain levels. That is, experiments must be conducted in the linear viscoelastic region.

Using an ARES Rheometer to investigate the β-relaxation change of graphene poly(ethyl methacrylate) nanocomposite

Here we describe the application of an ARES Rheometer (TA Instruments) with a rectangular torsion fixture, to investigate the β-relaxation change of poly (ethyl methacrylate)/ graphene oxide. It is observed that graphene increases both the glass transition and the β-relaxation temperature, but the β-relaxation to a lesser extent.

Preventing Wall Slip in Rheology Experiments

Wall slip is a common problem when testing highly concentrated emulsions or suspensions on a rheometer. It is usually caused by large velocity gradients in a thin region adjacent to the wall. When slip occurs, the measured viscosity can be significantly lower than the actual viscosity of the sample. To overcome this influence, we have introduced a series of roughened surface geometries, such as crosshatched or serrated plates, which significantly improve the contact between the geometry and the sample to reduce slip.